DE 601 11 162 T2 (corresponds to EP 1 208 940 B1) discloses a machine tool with a tool turret for the machining of metallic workpieces. Through the tool turret, a cryogenic cooling medium is carried to the respective tool that is momentarily in engagement with the workpiece to be machined. For this purpose, the tool turret has a polymer rotor with a first thermal expansion coefficient and an associated metallic stator with a second thermal expansion coefficient. A first feed line runs through the stator, which has a first section running concentrically to the axis of rotation of the rotor and a second line section running radially with respect to the rotary axis. In the working position of the respective tool, the first feed line is connected to an associated second feed line that runs through the rotor, which surrounds the stator, to the tool. Because of the different thermal expansion coefficients, the feed lines are automatically sealed at the connecting points when the cryogenic cooling medium flows through the feed line to the respective tool. The problem with this tool turret is that it is difficult to seal the connection between the feed lines since, on the one hand, the stator must be pressed with adequate force against the rotor for sealing the connection because of the different expansion coefficients, but on the other hand, the force must not be too high since otherwise the tool turret jams and a tool change is no longer reliably possible. This is especially a problem if a cryogenic cooling medium and/or different cryogenic cooling media with different temperatures are used, since the expansion behavior of the stator and the rotor can be dissimilar.
The invention is based on the object of producing a tool turret in which a cryogenic cooling medium can be supplied to the tools in a simple and reliable manner.
This object is achieved by a tool turret with a first feed line that can be moved, at least in sections, by means of a linear actuator parallel to the rotary axis so that a simple and reliable transfer of the cryogenic cooling medium is possible up to the tool that is in engagement with the workpiece to be processed and, in addition, a simple and reliable tool change is possible. The first feed line is connected so that in its first position it is sealed with the second feed line of the associated tool of which is currently in the work position for machining the workpiece. The cryogenic cooling medium can be transferred simply and reliably to the tool. For a tool change, the first feed line is moved by means of the linear actuator into its second position, in which the first feed line is disconnected from the second feed lines. In the second position, the rotary position of the rotating part with the tool holders is thus simply and reliably changed for the tool change. After the tool change, the first feed line is moved again by means of the linear actuator into the first position in which it is connected and sealed with the second feed line of the new tool located in the work position.
The tool turret according to the invention makes possible a simple and reliable feed of a cryogenic cooling medium independently of its temperature. At the outlet of the respective tool, the cryogenic cooling medium has a temperature of less than −60° C., and may be less than −120° C., and may be less than −150° C., and may be less than −180° C. As cryogenic cooling medium, for example liquid or gaseous nitrogen, liquid or gaseous oxygen, gaseous hydrogen, gaseous helium, liquid or gaseous argon, gaseous carbon dioxide and liquid or gaseous natural gas can be used. Preferably nitrogen is guided through the feed lines to the tools. In addition—if necessary—a non-cryogenic cooling lubricant can also be supplied through the tool turret to the respective tool.
Because of the fact that the cryogenic cooling medium is supplied directly up to the cutting edge of the tools and these are effectively cooled because of the extremely low temperature of the cryogenic cooling medium, higher cutting speeds during workpiece machining are possible in comparison to the usual cooling lubricants. In addition, the cryogenic cooling medium has a positive effect on the service lives of the tools. The productivity and cost-effectiveness of the workpiece machining can be increased correspondingly by the supply of the cryogenic cooling medium to the cutting of the tools. Since the cryogenic cooling medium evaporates, neither the processed workpieces nor the tool turret and/or the entire machine tool becomes soiled. Disposal of the cryogenic cooling medium as is required with the usual cooling lubricants is no longer necessary, whereby the cost-effectiveness of the workpiece machining is even further improved.
In a simple manner, the tool turret ensures that the cryogenic cooling medium is not heated to an undesirable extent on the way to the tools and the components of the tool turret surrounding the first feed line do not cool to an extent that is not permissible. In this way, the tools can be extremely effectively cooled and at the same time thermal tensions in the components surrounding the first feed line can be prevented. Preferably, the first feed line is designed so that it is completely insulated, i.e. thermally insulated over the entire length. For example, the feed line has an inner pipe and an outer pipe surrounding it that is connected with it at the end. The insulation space defined by the pipes is filled, for example, with an insulation medium. If the first feed line is designed so that it is vacuum-insulated, the insulation space is evacuated, whereby the feed line has an extremely low specific heat conductivity. The first feed line may have a specific heat conductivity at 0° C. of max. 0.40 W/(mK) [watts per meter Kelvin], especially of max. 0.30 W/(mK), and especially of max. 0.20 W/(mK). If the first feed line is designed so that it is vacuum-insulated, its specific heat conductivity is extremely low and at 0° C. is maximum 0.01 W/(mK). Preferably the second feed lines are also thermally insulated, at least in sections, and may be vacuum-insulated. The statements for the first feed line then also apply to the second feed lines.
The tool turret makes possible a compensation of the different length changes of the inner and outer pipes. If the first feed line has the cryogenic cooling medium flowing through it, the inner pipe essentially assumes its temperature, while in contrast the outer pipe cools less because of the insulation medium arranged between the two pipes. The inner pipe changes its length more than the outer pipe. In order to prevent damage of the first feed line, at least one of the pipes must have a changeable length. Preferably the outer pipe has a serpentine shaped metal boot for thermal length compensation. In particular, the second feed lines also each have an inner pipe and an outer pipe surrounding them, whereby at least one of these pipes is changeable in length. The statements regarding the first feed line apply equally to the second feed lines designed in this way.
The tool turret ensures high thermal insulation of the two feed lines in order to prevent undesirable heating of the cryogenic cooling medium on the way to the tools. Preferably the second feed lines are each completely insulated, i.e. thermally over the entire length. Otherwise the statements regarding the first feed line apply equally to the second feed line.
The tool turret makes possible, in a simple manner, a connecting and disconnecting of the feed lines for transferring the cryogenic cooling medium and for a tool change. For connecting the feed lines, the first feed line is displaced in a linear manner in a first direction by means of the double-acting piston-cylinder unit, while in contrast for tool change the first feed line is displaced in a linear manner by means of the piston-cylinder unit in a second, opposite direction. Preferably the piston-cylinder unit can be actuated pneumatically or hydraulically. The respective position of the piston-cylinder unit is preferably detected by means of at least one sensor.
The tool turret ensures a simple and reliable connection of the feed lines. Because of the funnel-shaped design, the first feed line can be introduced in a simple way into the second feed line and sealed at the connecting point. For this purpose, for example after the funnel-shaped end section, a gasket can extend into the respective second feed line through which the first feed line is introduced. In addition, the funnel-shaped end section itself is designed as a gasket. The gaskets have an especially high resistance to the cryogenic cooling medium. Preferably the gaskets are made of a plastic material and/or a rubber material that has high chemical resistance and good thermal insulation properties. Preferably the gaskets are made of PTFE (polytetrafluoroethylene).
The tool turret ensures a simple feed of the cryogenic cooling medium. Because of the fact that the first feed line is at a distance from the axis of rotation, i.e. preferably outside the housing, the second feed lines can be designed so they are extremely short.
In a second embodiment, the tool turret ensures a simple and reliable feed of the cryogenic cooling medium to the tools. Because of the fact that the respective first line section runs parallel to the axis of rotation, the first feed line can be connected to the respective second feed line by a simple linear movement. Since the respective second line section runs perpendicularly and/or radially with respect to the axis of rotation, the cryogenic cooling medium is supplied directly up to the cutting edge of the tools.
In the second embodiment, because of the design of the first feed line, only the second line section is moved perpendicularly and/or radially with respect to the axis of rotation by means of the linear actuator. The first line section that runs concentrically to the axis of rotation is mounted fixed in the axial direction. Since neither the first line section nor the second line section is formed in the rotating part, these are also fixed during a rotation of the rotating part. Because of the arrangement of the first feed line, the structure of the tool turret is extremely compact.
In the second embodiment, because of the fact that the second feed lines each run exclusively perpendicularly and/or radially with respect to the axis of rotation, the cryogenic cooling medium can be guided directly to the cutting edge of the tools.
In the second embodiment, the tool turret ensures, in a simple and reliable manner, a cooling of rotary-drivable tools. The tool mount that is rotary-drivable by means of the drive motor is rotary driven around the associated second feed line, which is arranged concentrically to the tool axis of rotation and does not rotate with the tool mount around the tool axis of rotation. Thus, by means of the tool mount, the tool can be rotary driven around the associated tool axis of rotation and at the same time, in a simple and reliable manner, the cryogenic cooling medium can be supplied to the cutting edge of the rotary driven tool. For example, as a rotary-driven tool, a drill can be used in the tool mount which is driven together with the drill. In addition, tools can also be used in the tool mount that are not rotary driven. For example, in the tool mount, a lathe chisel can be used as a tool, which during the machining is not rotary driven by means of the drive unit, i.e., is fixed around the tool axis of rotation.
In the second embodiment, the tool turret ensures a reliable feed of the cryogenic cooling medium since the respective second feed line does not rotate around the tool axis of rotation and, corresponding to the first feed line, is arranged fixed around the tool axis of rotation.
The invention is also based on the object of producing a machining system that makes possible a simple and reliable feed of the cryogenic cooling medium to the tools.
The advantages of the machining system according to the invention correspond to the advantages already described of the tool turret. From the thermally insulated reservoir, the cryogenic cooling medium is fed through the thermally insulated supply line to the tool turret. In order to keep the temperature of the stored cryogenic cooling medium constant, a cooling unit is provided. In addition, the machining system has a feed pump to pump the cryogenic cooling medium from the reservoir to the tool turret. For the tool change, the machining system also has a shutoff valve that interrupts the supply of the cryogenic cooling medium to the tool turret before a tool change. The cooling unit and/or the feed pump and/or the shutoff valve can be controlled by means of a control device. The machining system is part of an otherwise usual machine tool for the machining of metallic workpieces, especially of shaft-like workpieces.
Other characteristics, advantages and details of the invention will be seen from the following description of several exemplary embodiments.